The present invention relates to improvements in the operating efficiency of refrigeration equipment used in the manner of a heat pump.
The vapor compression refrigeration cycle has been used in applications which may utilize either the cooling effect produced at the evaporator or the heating effect produced at the condenser. In the second application the system is commonly referred to as a heat pump although it employs the same elements as a refrigeration system concerned only with the low temperature effect produced at the evaporator. That is, either system normally comprises a compressor, condenser, evaporator/chiller, throttling valves as well as appropriate controls and piping, the main difference being in the primary objectives of the application and the method of system operation. Commonly, the same system is utilized with the dual objectives of providing cooling during the cooling season and heating during the heating season.
When the heat pump operates as a heating system, heat is removed from the outdoor air, water or other such low-temperature heat source by evaporation of the refrigerant and delivered, together with the heat equivalent of the work of compression, to the space to be heated. Natural water supplies, such as lakes, rivers or bays, offer convenient sources from which heat may be extracted, but the amount of permissible temperature drop is often quite low. That is, during the winter months in many parts of the world, when the heat pump using a water source would be most useful as a heating system, the temperature of natural water supplies is often below 40.degree. F. Since the water must remain above 32.degree. F as it passes through the system before being returned to the source, the amount of heat which may be extracted is obviously quite limited. Accordingly, the heat pump using natural water sources is not commonly employed as a heating system on a wide commercial scale, other systems being more practical.
Electrical generating plants are often powered by steam turbines. A fuel is burned to provide heat to the boiler, producing steam. The energy given up by the steam as it passes through the turbine stages drives the turbine. After leaving the last stage of the turbine the steam is exhausted to a condenser where it is returned from the vapor to the liquid state. Water is circulated through the steam condenser to act as a medium of heat exchange, absorbing the heat given up by the steam during condensation.
The water used in the steam condenser may conveniently be taken from a lake, river, or other natural source, and is usually discharged back to the same source after undergoing a temperature rise in the condenser. It is not uncommon, for example, for water used in the condenser of a steam turbine generating plant to rise by 30.degree. or more from inlet to discharge. The marine quality of many natural bodies of water has been adversely affected by "thermal pollution" resulting from the discharge of heated water from power plant condensers into natural bodies of water.